Contamination of soil and groundwater by various compounds including both organic and inorganic chemicals is widespread. This contamination threatens human health, public safety, public welfare and the environment. Attempts to remediate contaminated soil or groundwater by a variety of means are common.
One common technique for decontaminating aquifers that is in current use is the pump-and-treat method. As practiced, this method utilizes a series of extraction wells drilled into a contaminated aquifer. Contaminated water is drawn through an extraction well, treated to remove or degrade the contaminant, and then returned to the aquifer through one or more injection wells or discharged to sewers or other points of non-origin. This method can be time consuming and cost-prohibitive.
Two other existing in situ methods of remediation of contaminated soil or groundwater are chemical treatment and biological treatment. Typically, chemical treatment consists of oxidation or reduction of the contaminants via application of remedial additives which can include, but are not limited to, hydrogen peroxide, Fenton's Reagent, ozone, sodium persulfate, sodium or potassium permanganate or lactate. Typically biological treatment consists of stimulating microorganisms that are either naturally occurring at the treatment location or microorganisms that are introduced into the treatment area. Stimulation is achieved by altering nutrient and electron acceptor concentrations in a manner that is beneficial to the microorganisms.
The efficiency of both chemical and biological treatment largely depends on the remedial additives being in contact with the contaminants in the environmental media being treated. Existing methods of applying remedial additives typically relies on groundwater dispersion of the remedial additives from the point of introduction or release, where the groundwater flow may travel beyond the target area. Accordingly, the remedial additives are, in part, transported to locations other than those locations targeted for remedial action. This groundwater transport most commonly results from advection and dispersion in water. The large-scale dispersion reduces the efficacy of the chemical or biological treatment of the contaminants because the dispersed remedial additives are no longer co-located with the contaminants and further reduces the efficacy of the treatment as the dispersion reduces the concentrations of the remedial additives.
Additional complexity in remedial treatment results from the existence of contaminants that have limited solubility in water, such as petroleum hydrocarbons or halogenated hydrocarbons. In the environmental remediation field, petroleum hydrocarbons typically refer to, but are not limited to, gasoline, oils, petroleum solvents such as benzene and various synthetic additives commonly used in gasoline or oils. Halogenated hydrocarbons are compounds composed of hydrogen and carbon with at least one hydrogen substituted by a halogen atom (e.g. Cl, Br, or F). Halogenated hydrocarbons are used for many purposes, such as solvents, pesticides, and degreasers. Degreasing products have widespread use in several industries, including dry cleaning, microelectronics, and equipment maintenance. Some of the most common halogenated hydrocarbons are methylene chloride, chloroform, carbon tetrachloride, tetrachloroethene (PCE), trichloroethene (TCE), 1,1,1-trichloroethane (TCA), dichloroethene (DCE), and vinyl chloride (VC). Such compounds are commonly known as “chlorinated hydrocarbons” or “chlorinated solvents.”
The limited solubility of petroleum hydrocarbons or halogenated hydrocarbons and density differential between water and either petroleum hydrocarbons or halogenated hydrocarbons greatly complicates environmental remediation. When released these compounds migrate as a non-aqueous liquid through soil, sediment or bedrock under density-driven flow. The compounds will migrate in a manner that is controlled by their density and the heterogeneities of the media they are migrating through. The compounds will, to varying degrees, interact with water present. In the case of the petroleum hydrocarbons, which are typically less dense than water, they will migrate vertically through the soil, sediment or bedrock and follow a pathway of least resistance until a zone of high water saturation is encountered. Migration will then have a significantly reduced vertical migration component and an increased horizontal component. The petroleum hydrocarbons will tend to accumulate immediately above the zone of increased water saturation. In the case of a groundwater system, this will be on water table or immediately above the water table, in the zone of partial saturation commonly referred to as the capillary fringe. In the case of halogenated hydrocarbons, which are typically denser than water, the vertical migration of these compounds is not substantially impeded by the presence of the water table. Vertical migration continues controlled primarily on density flow and heterogeneities in the subsurface medium.
Both petroleum hydrocarbons and halogenated hydrocarbons can be present in environmental media as Non-Aqueous Phase Liquids (NAPLs). In the case of NAPL compounds that are less dense than water, such compounds are referred to as “Lighter NAPLs” or “LNAPLs.” In the case of compounds that are denser than water, such compounds are called “Dense NAPLs” or “DNAPLs.” NAPLs can be found on a large scale as LNAPLs floating on the groundwater table in a measurable thickness or as DNAPLs which accumulate on a stratigraphic feature either above or below the groundwater table. On a smaller scale NAPLs can be found adsorbed to individual soil grains or on other subsurface structures.
Both chemical oxidation and bioremediation are less successful in the vadose zone soils located above the water table. This is in part due to the water-based remedial additives used in these methods being placed subsurface, resulting in these remedial additives draining through the vadose zone soils. Such drainage does not allow sufficient contact time between the remedial additives and the contaminated soils for optimal remedial effects. In contaminated soil or groundwater located below the groundwater table, the groundwater itself dilutes and disperses the remedial additives.
The drainage and/or dispersion can also result is less efficient treatment; in part because the remedial additives may be transported to locations where little or no contamination is present, as well as reducing the concentration of the remedial additives where they are most desired. This decreases the efficiency of both chemical oxidation and bioremediation in permeable sediments and bedrock.
Another problem with the inefficient dispersion in existing methods and formulations is that the introduction of remedial additives in uncontaminated media can degrade groundwater and/or soil quality, or under some circumstances, can contaminate previously unaffected areas.
In U.S. Pat. No. 4,591,443, Brown and Norris provide for a method of altering the viscosity of a chemical oxidation formulation by adding hydratable polymeric material. Hydratable polymeric materials are commonly used in well drilling and other industries to control the viscosity of liquids. However, the various polymeric materials that are utilized in the '443 patent have limitations. Some of the polymers identified in the '443 patent have limited thermal stability: above certain temperatures, the viscosity modifiers lose their beneficial properties. In efforts to avoid this the '443 patent proposes use of various cross-linking compounds. Both the polymeric materials and the cross-linking compounds as identified in the '443 patent can themselves be environmental contaminants. These compounds can also react with, and therefore reduce the efficiency of, the chemical oxidation reactants that they are designed to deliver. The '443 patent does not disclose viscosity modification as being potentially beneficial to bioremediation efforts. This lack of disclosure may be because the viscosity modifiers proposed in '443 can either cause additional oxygen demand as they degrade or be toxic to the microorganisms necessary for bioremediation, thus reducing the efficiency of or preventing bioremediation. In fact, some or all of the viscosity modifying agents proposed under '443 may themselves be viewed as environmental contaminants and require subsequent removal or treatment. This subsequent need for removal or treatment can eliminate or reduce any efficiency in the treatment of the original contaminants.
The present invention provides an improvement over the limitations of '443 and an extension of viscosity modification to treatments other than chemical oxidation.
It is the object of the present invention to provide an improved formulation for remedial additives to be introduced into environmental medium.
It is another object of the present invention to overcome the shortcomings and inefficiencies of prior art remedial additive introduced into a variety of environmental media.
It is another object of the present invention to improve the efficiency of chemical treatment, biological treatment or the integration of the two by allowing the remedial additives to be focused in the desired treatment zone. This focusing results from the viscosity of the formulation, the dissolution of the formulation over time and the ability to introduce the formulation in a manner that follows preferential migration pathways in the environmental media.
It is another object of the present invention to improve efficiency of remediation by formulating remedial additives that can be made to migrate through environmental media in a manner similar to contaminants, thereby better co-locating of the remedial additives with the contaminants to be treated.
It is another object of the present invention to provide a formulation that allows greater control over the placement of the remedial additives than is otherwise possible.
It is another object of the present invention to provide a formulation for remediation of contaminated areas that reduces the likelihood of accidental contamination of previously uncontaminated environmental media.
It is another object of the present invention to provide a formulation for remediation of contaminated areas that reduces the need for post-remediation cleanup of the formulation itself.
It is yet another objective of the present invention to provide an improved, safer, more cost-efficient method for remediation of environmental contaminants.